During the past months, I developed Lyra, an incredibly fast full-text search engine entirely written in TypeScript. It was surprising to me to see how it could compete with solutions written in Rust, Java, and Golang, all languages known for being typically "faster than JavaScript"... but is that even true? In this talk, I will share some lessons I learned while developing complex, performance-critical applications in JavaScript, starting from the reasons why JavaScript is very difficult to benchmark, and how to truly understand its performance.